Former Texas Gov. Rick Perry testifies before a Senate Energy and Natural Resources Committee hearing on his nomination to be Energy secretary at Capitol Hill in Washington, January 19, 2017. REUTERS/Carlos Barria

WASHINGTON – Rick Perry, President-elect Donald Trump's nominee to run the Energy Department, expressed contrition for campaigning on the promise of doing away with the agency at his confirmation hearing before the Senate Committee on Energy and Natural Resources, which kicked off Thursday morning.

"My past statements made over five years ago about abolishing the Department of Energy do not reflect my current thinking," Perry said in his opening statement. "In fact, after being briefed on so many of the vital functions of the Department of Energy, I regret recommending its elimination."

After addressing the defining moment of his national political career, Perry touched on the politically sensitive topic of climate change, saying he believes the climate is changing and "some of it" is caused by "man-made activity." He added: "The question is how we address it in a thoughtful way that doesn't compromise economic growth."

With his acknowledgement of climate change and its causes, Perry went further than Trump did in a television interview broadcast late last year. The president-elect told "Fox News Sunday" in December that "nobody really knows" whether climate change is real.

Perry also tried to defuse controversy over a questionnaire the Trump transition team gave to Energy Department officials asking for the names of individuals involved in climate change research and negotiations. Though the transition team disavowed the questionnaire, it raised fears of a witch hunt for people working on climate change.

"That questionnaire went out before I was ever selected," Perry said. "I didn't approve it. I don't approve of it. I don't need that information. I don't want that information." He added, "I have a history of working with people to deal with the challenges that face us."

Perry also sought to reassure the Senate panel about the prospect that the Trump transition team would demand the resignation of Lt. Gen. Frank G. Klotz, a political appointee heading the Energy Department's National Nuclear Security Administration. Perry said he met with Klotz and has asked Trump to leave Klotz in place to assure "continuity in these very important places."

The hearing took a lighter turn when Sen. Al Franken, D-Minn., started questioning Perry.

"Did you enjoy meeting me?" Franken asked.

"I hope you are as much fun on that dais as you were on your couch," Perry responded. The room erupted in laughter.

But the mood quickly turned serious when Franken cited Perry writing about a "cooling trend" in his 2010 book and asked him about how much climate change he thinks is due to human activity.

"Far from me to be sitting before you today and claiming to be a climate scientist. I will not do that," said Perry, dodging the question.

"I don't think you're ever going to be a climate scientist. But you're going to be the head of the Department of Energy," Franken shot back, before underscoring the consensus among scientists about temperature increases.

Trump's nomination of Perry marks an unusual turn for the Texas politician.

Former Texas Gov. Rick Perry testifies before a Senate Energy and Natural Resources Committee hearing on his nomination to be Energy secretary at Capitol Hill in Washington, January 19, 2017. REUTERS/Carlos Barria

As Perry bowed out of the presidential campaign in September 2015, the former Texas governor took a not so veiled parting shot at front-runner Donald Trump.

"The conservative movement has always been about principles, not personalities," Perry said in an email to supporters, urging them to vote for a candidate true to those principles. "Our nominee should embody those principles. He – or she – must make the case for the cause of conservatism more than the cause of their own celebrity."

Sixteen months later, Perry has been invited to join the cast of the Trump Cabinet as energy secretary. Perry, once a rising GOP star who crashed miserably in the 2012 presidential campaign, tried to resurrect his political career without success in 2016. An early critic of Trump, whose campaign he called a "barking carnival act," Perry found no audience. But now, thanks to President-elect Donald Trump, he is suddenly back in the mix.

The Energy Department is an unexpected landing pad for Perry. In the 2012 campaign, Perry said that the agency was one of three departments that should be abolished – though, with a sheepish "Oops," he famously could not remember its name during a debate. The episode marked the end of that campaign.

Now, Perry needs to figure out how to manage that department. If confirmed by the Senate, Perry would run an agency tasked with monitoring the nation's nuclear stockpile, cleaning up old nuclear weapons development sites, managing the strategic petroleum reserve, setting appliance standards, managing the national laboratories and overseeing a portfolio of grants, loans and loan guarantees that support research and development on every type of energy.

Many people say that Perry, despite his past vow to dismantle the department, has valuable experience for running it. As governor, he benefited from a rapid expansion of oil and gas exploration in new shale oil and shale gas plays. But he also oversaw an expansion of transmission lines that made way for a rapid expansion of wind energy.

"Under Rick Perry's leadership, Texas created a stable, long-term, competitive energy market, combined with robust infrastructure investment, which allowed new technologies, like wind, to enter," the American Wind Energy Association's chief executive, Tom Kiernan, said in a letter to the Senate Energy and Natural Resources Committee.

During Perry's tenure, Texas became the nation's leading wind energy state. In 2000, Texas wind energy production was 200 megawatts. By the end of 2015, the state had nearly 18,000 megawatts of installed capacity, driven by more than $32 billion of private investment in wind farms.

Perry's decision to support expansion of the Texas electric transmission lines spurred almost $7 billion in areas such as western Texas.

Environmental groups are less enthusiastic. Perry has sharply criticized Gov. Andrew M. Cuomo, D-N.Y., for banning hydraulic fracturing, or fracking, to explore for shale oil and shale gas. "I don't understand why a governor like Governor Cuomo, who is a smart and thoughtful individual, would allow a small group of radical environmentalists to stop job creation and to stop people's ability to have a better life for themselves," Perry said in a radio interview with a New York Post columnist.

Environmental groups have also pointed to Perry's campaign contributions. "Dirty energy interests have given Perry more than $13 million in campaign contributions," said Rhea Suh, president of the Natural Resources Defense Council. Despite the wind jobs created in his state, Perry "repeatedly claimed that protecting the environment kills jobs," Suh said.

The Nuclear Energy Institute, however, supports Perry. "Perry knows the vital role that nuclear energy plays in America's diverse electricity portfolio," NEI spokesman John Keeley said in an email. "His familiarity with used nuclear fuel storage issues as Texas governor gives him a running start in addressing DOE's nuclear waste management obligation."

Though Perry, who served as governor for 15 years, lacks the academic firepower of Massachusetts Institute of Technology physicist Ernest Moniz or Nobel Prize-winning physicist Steven Chu, other energy secretaries have included a U.S. senator, a business woman, a retired admiral and a dentist-turned-politician.

"He's managed one of the largest economies based on energy in the world," said Frank Maisano, a public affairs specialist in energy companies at the law firm Bracewell. "He did an effective job of balancing both fossil fuels and the expansion of renewable generation."

Salo Zelermyer, a senior lawyer at the Energy Department under President George W. Bush, said: "From my perspective, anybody who has served as governor of a state like Texas for the length of time he served speaks to his ability to manage large organizations and to understand the dynamic between the appropriate role of regulation and appropriate role of industry."

Yet lawmakers will likely highlight some sensitive issues during the hearing.

Democrats are expected to pepper Perry with questions about climate change and climate research, according to one Democratic Senate aide. Cybersecurity of the electricity grid could also come up.

Some environmental groups worry that Perry will try to curb the department's climate-related research and regulatory activities. President Barack Obama's two energy secretaries, Chu and Moniz, have both tried to steer the national laboratories toward research on technology that might help avert a climate catastrophe.

Perry might also have to deal with whether to restart work on the Yucca Mountain waste repository in Nevada that was halted by Obama.

He inherits the grant, loan and loan guarantee program that outgoing Secretary Moniz, has spread among projects as varied as carbon capture and battery research. Moniz treats it like a research and development fund, but many Republicans have condemned the program as picking winners and losers.

Members of the Senate panel will likely ask about the slow cleanup of radioactivity at the Hanford, Washington, site where the government produced plutonium for weapons and conducted research for the first nuclear bombs.